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I would like to be able to perform the following, but it fails in the call to useMap. How can I perform this conversion?
scala> import scala.collection.JavaConversions._ import scala.collection.JavaConversions._ scala> import scala.collection.JavaConverters._ import scala.collection.JavaConverters._ scala> def useMap(m: java.util.Map[java.lang.Integer, java.lang.Float]) = m useMap: (m: java.util.Map[Integer,Float])java.util.Map[Integer,Float] scala> val v: Map[Int, Float] = Map() v: Map[Int,Float] = Map() scala> useMap(v) <console>:10: error: type mismatch; found : scala.collection.immutable.Map[Int,scala.Float] required: java.util.Map[Integer,java.lang.Float] useMap(v) ^ It seems to work with Map[String, String], but not Map[Int, Float].
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To convert, Java Map to Set , we can use the conventional constructor with HashSet , however, there are few things to consider before we proceed with the conversion.
In Scala, you can convert a list to a map in Scala using the toMap method. A map contains a set of values i.e. key-> value but a list contains single values. So, while converting a list to map we have two ways, Add index to list.
Maps are classified into two types: mutable and immutable. By default Scala uses immutable Map. In order to use mutable Map, we must import scala.
HashMap is a part of Scala Collection's. It is used to store element and return a map. A HashMap is a combination of key and value pairs which are stored using a Hash Table data structure. It provides the basic implementation of Map.
The solution linked to by @pagoda_5b works: Scala convert List[Int] to a java.util.List[java.lang.Integer]
scala> import collection.JavaConversions._ import collection.JavaConversions._ scala> val m = mapAsJavaMap(Map(1 -> 2.1f)).asInstanceOf[java.util.Map[java.lang.Integer, java.lang.Float]] m: java.util.Map[Integer,Float] = {1=2.1} scala> m.get(1).getClass res2: Class[_ <: Float] = class java.lang.Float Use scala predefined float2Float and use CollectionConverters to perform conversion explicitly.
import scala.jdk.CollectionConverters._ // Prior to Scala 2.13: import scala.collection.JavaConverters._ val scalaMap = Map(1 -> 1.0F) val javaMap = scalaMap.map{ case (k, v) => k -> float2Float(v) }.asJava If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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